docs: def source_data_key_length_check(source_data_key, algorithm):
      """Validates that the supplied source_data_key's data_key is the
      correct length for the supplied algorithm's kdf_input_len value.
  
      :param source_data_key: Source data key object received from MasterKey decrypt or generate data_key methods
      :type source_data_key: :class:`aws_encryption_sdk.structures.RawDataKey`
          or :class:`aws_encryption_sdk.structures.DataKey`
      :param algorithm: Algorithm object which directs how this data key will be used
      :type algorithm: aws_encryption_sdk.identifiers.Algorithm
      :raises InvalidDataKeyError: if data key length does not match required kdf input length
      """
      if len(source_data_key.data_key) != algorithm.kdf_input_len:
          raise InvalidDataKeyError(
              "Invalid Source Data Key length {actual} for algorithm required: {required}".format(
                  actual=len(source_data_key.data_key), required=algorithm.kdf_input_len
              )
          )